The present invention is related to a resin composition to which flame retardancy is conferred, particularly a resin composition containing a biodegradable resin and/or a resin whose material is plant resource, or a polystyrene resin, and a method for producing the resin composition, and a method for molding the resin composition.
Recently, attention is paid to a resin (or plastic) which is degraded by a bacterial action when it is buried in the ground. The resin which is referred to as a biodegradable resin (or a biodegradable plastic) has a characteristic of being degraded under the presence of aerobic bacterial into water (H2O) and carbon dioxide (CO2). The biodegradable resin has been put to practical use in an agricultural field, and has been practically applied as a packaging material of a disposable article and a compostable garbage bag.
When the biodegradable resin is subjected to waste disposal by utilizing its characteristic of being degraded with the bacteria in the ground, it is possible to significantly reduce emission of CO2 compared with conventional incineration. Therefore, attention is paid to the use of the biodegradable resin from the view point of the prevention of global warming. The article wherein the biodegradable resin is used may be advantageous to the user because it is unnecessary to collect a used plastic when the article is used in the agricultural field. For these reasons, the market of the biodegradable resin is expanding.
Further, attention has been recently paid to also a plant-based (or plant-derived) resin in the fields of electronics and automobile. The plant-based resin is obtained by polymerizing or copolymerizing monomers which are obtained from plant materials. The plant-based resin draws attention as an environment-friendly resin because it is produced without relying on petroleum resources, the plant which is a material for the resin grows absorbing carbon dioxide, and a burned calorie and a CO2 emission are small when it is disposed of with an incinerator. The plant-based resin generally has biodegradability. The plant-based resin, however, does not necessarily need to have biodegradability only from the viewpoint of the prevention of depletion of petroleum resources. In other words, resins which contribute to environmental protection include the plant-based resins which do not have biodegradability, in addition to the biodegradable resins. For this reason, in the specification including the following description, a term “environmental resin” is used for the sake of convenience in order to give a generic name to the biodegradable resins (including petroleum-based ones and the plant-based ones) and the plant-based resins which do not have the biodegradability.
The environmental resins which are now used are classified roughly into three types, a polylactic acid-based resin (hereinafter, it is abbreviated as a “PLA”), a PBS-based resin (a copolymer resin of 1,4-butanediol and succinic acid), and a PET-based resin (modified polyethylene terephthalate). The characteristics of each resin are shown in Table 1.
TABLE 1PET-basedPLAPBS(Modified(Polylactic(Polybutylenepolyethyleneacid)succinate)terephthalate)Biodegradability⊚⊚◯MaterialPlantPetrochemicalPetrochemicalfeedstocksfeedstocksA synthesize method with aplant material is reported.
Among these resins, the PLA corresponds to the plant-based resin. The PLA can be produced by a chemical synthesis by using, as a material, sugar made by plant such as corn or sweet potato, and there is a possibility of industrial production of the PLA. Such a plastic containing the plant-based resin is also referred to as a bio plastic. Particularly the PLA draws attention since mass production thereof has been started using corn as a material. It is desired that a technique of applying the PLA not only to a use which requires biodegradability, but also to a wide variety of uses is developed.
It is, however, necessary to improve the characteristics of these environmental resins for substituting them for existing materials. The physical properties of polystyrene (PS) and an acrylonitrile-butadiene-styrene resin (hereinafter, it is abbreviated as “ABS”) which are general resins and the physical properties of polylactic acid (PLA) and polybutylene succinate (PBS) which are the environmental resins are shown in Table 2. A “bending modulus” and a “bending strength” represent rigidity. As these values are higher, the rigidity is higher. An “izod impact strength” represents a fracture energy when a test piece is subjected to an impact load to be broken. As the value of the “izod impact strength” is larger, the piece is more difficult to be broken when impact is applied. The “heat deformation temperature” is a temperature at which the resin starts to deform. As the value of the “heat deformation temperature” is higher, it is possible to use the resin under a higher-temperature condition.
TABLE 2EnvironmentalGeneral resinresinResinPSABSPLAPBSBending2250210045001950 modulusBending477013255strengthIzod8020046NDimpactstrengthHeat8096-1006697deformationtemperature
From this table, it is found that PLA is hard and fragile, and that PBS is soft. Further, it is found that PLA is poor in heat durability and that PBS has higher heat durability than ABS, as a result of comparison of the thermal characteristic.
A method which involves blending of another component has been proposed for improving the characteristics of these environmental resins. For example, it is proposed that a synthesized mica of about 0.5-20 wt % is blended with the PLA for the purpose of improving the heat resistance of PLA in Japanese Patent Kokai (Laid-Open) Publication No. 2002-173583(A) (Patent Literature 1). In the Japanese Patent Kokai (Laid-Open) Publication No. 2002-173583(A), it is proposed that an additive inhibiting hydrolysis of the biodegradable resin (that is, the biodegrading action), for example, a carbodiimide compound is blended.
Further, it is reported that there is a possibility of applying PLA to an exterior body of a personal computer when kenaf is blended with PLA (see Serizawa et al. “Development of polylactic acid reinforced by kenaf”, The 14th annual meeting of Japan Society of Polymer Processing pre-print materials, pp 161-162, 2003 (Non-patent Literature 1). Specifically, it is reported that the heat resistance of the PLA resin is improved by adding an annealing process after molding the PLA resin wherein kenaf is blended, so that there is a higher possibility of applying the PLA to the exterior body of the personal computer.
On the other hand, a polystyrene (PS) resin which is not the environmental resin, has good balance between physical properties and cost and it is widely used in products in various fields, such as containers and packaging, building material, sundry goods, electric equipment and electronic equipment, fiber, paint and adhesive, automobile, and precision mechanical equipment. The total used amount of polystyrene is also large, and polystyrene is one of five general-purpose resins, along with vinyl chloride, polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET). Therefore, it would be still necessary to use the polystyrene resin while developing the environmental resin. Not a conventional PS resin but a high impact polystyrene (HIPS) which is obtained by blending a butadiene rubber with PS is mainly used in consumer durable goods such as electric and electronic products, building material, and automobile among the above-mentioned applications. HIPS is further improved in impact resistance compared to PS and used for constituting parts or members, such as exterior bodies of various products which are used for a relatively long period.    Patent Literature 1: Japanese Patent Kokai (Laid-Open) Publication No. 2002-173583(A)    Non-patent Literature 1: Serizawa et al. “Development of polylactic acid reinforced by kenaf”, The 14th annual meeting of Japan Society of Polymer Processing pre-print materials, pp 161-162, 2003